Structural insights into Clostridium perfringens delta toxin pore formation

Clostridium perfringens Delta toxin is one of the three hemolysin-like proteins produced by C. perfringens type C and possibly type B strains. One of the others, NetB, has been shown to be the major cause of Avian Nectrotic Enteritis, which following the reduction in use of antibiotics as growth promoters, has become an emerging disease of industrial poultry. Delta toxin itself is cytotoxic to the wide range of human and animal macrophages and platelets that present GM2 ganglioside on their membranes. It has sequence similarity with Staphylococcus aureus β-pore forming toxins and is expected to heptamerize and form pores in the lipid bilayer of host cell membranes. Nevertheless, its exact mode of action remains undetermined. Here we report the 2.4 Å crystal structure of monomeric Delta toxin. The superposition of this structure with the structure of the phospholipid-bound F component of S. aureus leucocidin (LukF) revealed that the glycerol molecules bound to Delta toxin and the phospholipids in LukF are accommodated in the same hydrophobic clefts, corresponding to where the toxin is expected to latch onto the membrane, though the binding sites show significant differences. From structure-based sequence alignment with the known structure of staphylococcal α-hemolysin, a model of the Delta toxin pore form has been built. Using electron microscopy, we have validated our model and characterized the Delta toxin pore on liposomes. These results highlight both similarities and differences in the mechanism of Delta toxin (and by extension NetB) cytotoxicity from that of the staphylococcal pore-forming toxins

Boring bivalve traces in modern reef and deeper-water macroid and rhodolith beds

Macroids and rhodoliths, made by encrusting acervulinid foraminifera and coralline algae, are widely recognized as bioengineers providing relatively stable microhabitats and increasing biodiversity for other species. Macroid and rhodolith beds occur in different depositional settings at various localities and bathymetries worldwide. Six case studies of macroid/rhodolith beds from 0 to 117m water depth in the Pacific Ocean (northern Central Ryukyu Islands, French Polynesia), eastern Australia (Fraser Island, One Tree Reef, Lizard Island), and the Mediterranean Sea (southeastern Spain) show that nodules in the beds are perforated by small-sized boring bivalve traces (Gastrochanolites). On average, boring bivalve shells (gastrochaenids and mytilids) are more slender and smaller than those living inside shallow-water rocky substrates. In the Pacific, Gastrochaena cuneiformis, Gastrochaena sp., Leiosolenus malaccanus, L. mucronatus, L. spp., and Lithophaga/Leiosolenus sp., for the first time identified below 20m water depth, occur as juvenile forms along with rare small-sized adults. In deep-water macroids and rhodoliths the boring bivalves are larger than the shallower counterparts in which growth of juveniles is probably restrained by higher overturn rates of host nodules. In general, most boring bivalves are juveniles that grew faster than the acervulinid foraminiferal and coralline red algal hosts and rarely reached the adult stage. As a consequence of phenotypic plasticity, small-sized adults with slow growth rates coexist with juveniles. Below wave base macroids and rhodoliths had the highest amounts of bioerosion, mainly produced by sponges and polychaete worms. These modern observations provide bases for paleobiological inferences in fossil occurrences.Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) 25247083Erasmus+FAR2012-2017FIR2016FIR2018PRIN "Biotic resilience to global change: biomineralization of planktonic and benthic calcifiers in the past, present and future" 2017RX9XXXYBioMed Central-Prepay Membership at the University of FerraraJunta de Andalucía RNM 190Committee on ResearchMuseum of PaleontologyDepartment of Integrative Biology, UC BerkeleyUC Pacific Rim Projec

Ribonucleotide reductases of Salmonella Typhimurium : transcriptional regulation and differential role in pathogenesis

Ribonucleotide reductases (RNRs) are essential enzymes that carry out the de novo synthesis of deoxyribonucleotides by reducing ribonucleotides. There are three different classes of RNRs (I, II and III), all having different oxygen dependency and biochemical characteristics. Salmonella enterica serovar Typhimurium (S. Typhimurium) harbors class Ia, class Ib and class III RNRs in its genome. We have studied the transcriptional regulation of these three RNR classes in S. Typhimurium as well as their differential function during infection of macrophage and epithelial cells. Deletion of both NrdR and Fur, two main transcriptional regulators, indicates that Fur specifically represses the class Ib enzyme and that NrdR acts as a global repressor of all three classes. A Fur recognition sequence within the nrdHIEF promoter has also been described and confirmed by electrophoretic mobility shift assays (EMSA). In order to elucidate the role of each RNR class during infection, S. Typhimurium single and double RNR mutants (as well as Fur and NrdR mutants) were used in infection assays with macrophage and epithelial cell lines. Our results indicate class Ia to be mainly responsible for deoxyribonucleotide production during invasion and proliferation inside macrophages and epithelial cells. Neither class Ib nor class III seem to be essential for growth under these conditions. However, class Ib is able to maintain certain growth in an nrdAB mutant during the first hours of macrophage infection. Our results suggest that, during the early stages of macrophage infection, class Ib may contribute to deoxyribonucleotide synthesis by means of both an NrdR and a Fur-dependent derepression of nrdHIEF due to hydrogen peroxide production and DNA damage associated with the oxidative burst, thus helping to overcome the host defenses

Targeted Manipulation of Serotonergic Neurotransmission Affects the Escalation of Aggression in Adult Male Drosophila melanogaster

Dopamine (DA) and serotonin (5HT) are reported to serve important roles in aggression in a wide variety of animals. Previous investigations of 5HT function in adult Drosophila behavior have relied on pharmacological manipulations, or on combinations of genetic tools that simultaneously target both DA and 5HT neurons. Here, we generated a transgenic line that allows selective, direct manipulation of serotonergic neurons and asked whether DA and 5HT have separable effects on aggression. Quantitative morphological examination demonstrated that our newly generated tryptophan hydroxylase (TRH)-Gal4 driver line was highly selective for 5HT-containing neurons. This line was used in conjunction with already available Gal4 driver lines that target DA or both DA and 5HT neurons to acutely alter the function of aminergic systems. First, we showed that acute impairment of DA and 5HT neurotransmission using expression of a temperature sensitive form of dynamin completely abolished mid- and high-level aggression. These flies did not escalate fights beyond brief low-intensity interactions and therefore did not yield dominance relationships. We showed next that manipulation of either 5HT or DA neurotransmission failed to duplicate this phenotype. Selective disruption of 5HT neurotransmission yielded flies that fought, but with reduced ability to escalate fights, leading to fewer dominance relationships. Acute activation of 5HT neurons using temperature sensitive dTrpA1 channel expression, in contrast, resulted in flies that escalated fights faster and that fought at higher intensities. Finally, acute disruption of DA neurotransmission produced hyperactive flies that moved faster than controls, and rarely engaged in any social interactions. By separately manipulating 5HT- and DA- neuron systems, we collected evidence demonstrating a direct role for 5HT in the escalation of aggression in Drosophila

Comparing inequalities in the labour market from a segmentation perspective

Production of INCASI Project H2020-MSCA-RISE-2015 GA 691004The purpose of this chapter is to carry out a comparative analysis of labour markets in Europe and Latin America from the perspective of segmentation in order to explain the processes of social inequality that arise in the workplace, in light of recent trends in global socio-economic changes. The chapter proposes two main objectives. The first is to perform a comparative descriptive analysis of the main features of labour markets among 60 European and Latin American countries. The second objective is to propose a model of comparative analysis of labour inequality from the theoretical perspective of the segmentation of the labour market and structural heterogeneity. We will focus our analysis by selecting two countries, Spain and Argentina, which both underwent a late development of capitalism. The following general hypothesis is formulated: Spain and Argentina, having clearly differentiated features in economic structure, level of development, institutional frameworks and socio-historical processes, show common dynamics in the structuring of the capitalist labour market between a primary and secondary segment. Using equivalent databases on the workforce a typology of segmentation of employment is constructed that show, in addition to the specificities of each country, the similarities in the structuring of the labour market

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018.

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field